The same list of sizes is used for the Touch and the Glo, and I assume the Mini. The resolution makes the same size look smaller on the Glo. On the Touch, I use about 17 and the Glo about 22. So, the sizes that are roughly the same as print on the Touch are single-step sizes.

Oh, sheesh! Well, that seems like something they could very easily fix by having slightly different firmware (or just offering all the options for everyone), should they be so inclined. Fingers crossed they will.